A conventional radio communication receiver (hereinafter to be simply referred to as a receiver) will be explained below. In the communication environment of portable telephones or the like, there is risk of distortion in the reception signals due to frequency selective fading which involves intersymbol interference. Persons skilled in the art have used, in order to prevent occurrence of this type of distortion, a method of demodulating a signal by utilizing an intersymbol component with an equalizer.
A receiver which uses diversity reception in the communication environment of the above frequency selective fading has been disclosed in “A Maximum Likelihood Sequence Estimation Equalizer based on Maximal Ratio Combining” (1996 general meeting of The Institute of Electronic Information Communication Engineers of Japan, B-478), by Denno and Saito (“conventional example (1)”). According to this conventional example (1), signals of two systems are received, and a maximum likelihood sequence is estimated using one equalizer. In the estimation of the maximum likelihood sequence, branch metrics corresponding to respective reception signals are calculated, and the branch metrics of the two systems are combined, thereby to realize the diversity reception.
In the mean time, there is a technique, “Equalizer and Decoder, for Mobile Communication System” that is described in Japanese Patent Application Laid-open No. 2000-91967 (“conventional example (2)”). According to the conventional example (2), an error correcting section generates reliability information of a reception signal in simultaneous with an error correction processing. This reliability information is fed back to the equalizer, and the equalizer equalizes the signal again. The equalization processing and the error correction processing are repeated.
The conventional radio communication receivers described above have had the following problems.
In the conventional example (1), one equalizer demodulates the reception signals of the two systems. Therefore, at the time of manufacturing devices having different numbers of antennas in order to realize the diversity reception, it is necessary to design and manufacture the equalizers again by matching the numbers of the antennas. This results in high manufacturing cost.
It is possible to realize the equalizers using H/W like LSI's. However, in that case, since the reception signals of the two systems are received and the demodulation processing like Viterbi algorithm is required to be carried out, the wiring becomes complex and the packaging area becomes large.
According to the conventional example (2), it is not possible to implement the diversity reception. Since the diversity reception is not possible, there is a problem that the quality of the communication can not be improved.
It is an object of the present invention to provide a radio communication receiver which can realize the reduction in manufacturing cost and reduction in the packaging area, and which can improve communication quality as compared with the conventional technique even if diversity reception is employed.